Fill out target-spec metadata for all targets **What does this PR try to resolve?** This PR completes the target-spec metadata fields for all targets. This is required for a corresponding Cargo PR which adds a check for whether a target supports building the standard library when the `-Zbuild-std=std` flag is passed ([see this issue](https://github.com/rust-lang/wg-cargo-std-aware/issues/87). This functionality in Cargo is reliant on the output of `--print=target-spec-json`. **How should we test and review this PR?** Check that a given target-spec metadata has been updated with: ``` $ ./x.py build library/std $ build/host/stage1/bin/rustc --print=target-spec-json --target <target_name> -Zunstable-options ``` **Additional Information** A few things to note: * Where a targets 'std' or 'host tools' support is listed as '?' in the rust docs, these are left as 'None' with this PR. The corresponding changes in cargo will only reject an attempt to build std if the 'std' field is 'Some(false)'. In the case it is 'None', cargo will continue trying to build * There's no rush for this to be merged. I understand that the format for this is not finalised yet. * Related: #120745